Linux boot sequence stages, the GRUB bootloader, and basic boot troubleshooting concepts.
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- What is the first stage of the Linux boot process?
- BIOS or UEFI performs Power-on Self Test (POST) and hardware initialization.
- What does MBR stand for and what is its size limit?
- Master Boot Record; 512 bytes total, with 446 bytes for bootloader code.
- What is GPT and why is it preferred over MBR?
- GUID Partition Table; supports larger disks (over 2 TB) and more than 4 primary partitions.
- What is GRUB?
- GRand Unified Bootloader; the program that loads the Linux kernel into memory and passes control to it.
- Where is the GRUB2 configuration file located?
- /boot/grub/grub.cfg (generated from /etc/default/grub and /etc/grub.d/ scripts).
- What is the purpose of the /boot partition?
- Stores the kernel, initramfs, and bootloader files needed during system startup.
- What is the initramfs?
- A temporary root filesystem loaded into RAM before the real root filesystem is mounted.
- What does POST stand for in the boot process?
- Power-on Self Test; hardware verification performed by BIOS or UEFI before bootloader runs.
- What is the typical boot sequence order on a BIOS system?
- POST, bootloader (GRUB) from MBR, kernel loading, initramfs, systemd or init.
- How do you access the GRUB menu if it is hidden?
- Hold Shift key during boot (or Esc on some systems) to show the GRUB menu.
- What is single-user mode and how is it accessed via GRUB?
- A maintenance mode with no network and no other users; edit the kernel boot line and add 'single' or 's' parameter.
- What does the 'ro' parameter mean in GRUB boot options?
- Read-only; the root filesystem is mounted read-only initially, then remounted read-write by init.
- What does the 'rw' parameter mean in GRUB boot options?
- Read-write; the root filesystem is mounted directly with write permissions.
- What is the root parameter in GRUB used for?
- Specifies the device containing the root filesystem, e.g., root=/dev/sda1 or root=UUID=xxx.
- What does the 'quiet' boot parameter do?
- Suppresses most boot messages, showing only errors.